We revisit gradient-based optimization for infinite projected entangled-pair states, a tensor network ansatz for simulating many-body quantum systems. This approach is hindered by two major challenges: the high computational cost of evaluating energies and gradients, and an ill-conditioned optimization landscape that slows convergence. To reduce the number of optimization steps, we introduce an efficient preconditioner derived from the leading term of the metric tensor. We benchmark our method against standard optimization techniques on the Heisenberg and Kitaev models, demonstrating substantial improvements in overall computational efficiency. Our approach is broadly applicable across various contraction schemes, unit-cell sizes, and Hamiltonians, highlighting the potential of preconditioned optimization to advance tensor network algorithms for strongly correlated systems.

Quantum chemistry is envisioned as an early and disruptive application for quantum computers. Yet, closer scrutiny of the proposed algorithms shows that there are considerable difficulties along the way. Here, we propose two criteria for evaluating two leading quantum approaches for finding the ground state of molecules. The first criterion applies to the variational quantum eigensolver (VQE) algorithm. It sets an upper bound to the level of imprecision/decoherence that can be tolerated in quantum hardware as a function of the targeted precision, the number of gates and the typical energy contribution from states populated by decoherence processes. We find that decoherence is highly detrimental to the accuracy of VQE and performing relevant chemistry calculations would require performances that are expected for fault-tolerant quantum computers, not mere noisy hardware, even with advanced error mitigation techniques. Physically, the sensitivity of VQE to decoherence originates from the fact that, in VQE, the spectrum of the studied molecule has no correlation with the spectrum of the quantum hardware used to perform the computation. The second criterion applies to the quantum phase estimation (QPE) algorithm, which is often presented as the go-to replacement of VQE upon availability of (noiseless) fault-tolerant quantum computers. QPE requires an input state with a large enough overlap with the sought-after ground state. We provide a criterion to estimate quantitatively this overlap based on the energy and the energy variance of said input state. Using input states from a variety of state-of-the-art classical methods, we show that the scaling of this overlap with system size does display the standard orthogonality catastrophe, namely an exponential suppression with system size. This in turns leads to an exponentially reduced QPE success probability.

We report quantum oscillations in magnetoresistance that are periodic in magnetic field ($B$), observed at the interface between (${\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7}$)(${\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}$)${\mathrm{O}}_3$ and ${\mathrm{SrTiO}}_3$. Unlike Shubnikov–de Haas oscillations, which appear at magnetic fields $>7\mathrm{T}$ and diminish quickly as the temperature rises, these $B$-periodic oscillations emerge at low fields and persist up to 10 K. Their amplitude decays exponentially with both temperature and field, specifying dephasing of quantum interference. Increasing the carrier density through electrostatic gating results in a systematic reduction in both the amplitude and frequency of the oscillations, with complete suppression beyond a certain gate voltage. We attribute these oscillations to the Altshuler-Aronov-Spivak effect, likely arising from naturally formed closed-loop paths due to the interconnected quasi-one-dimensional conduction channels along ${\mathrm{SrTiO}}_3$ domain walls. The relatively long phase coherence length ($\simeq 1.8\mu \mathrm{m}$ at 0.1 K), estimated from the oscillation amplitude, highlights the potential of complex oxide interfaces as a promising platform for exploring quantum interference effects and advancing device concepts in quantum technologies, such as mesoscopic interferometers and quantum sensors.

The magnon orbital Hall effect in two-dimensional (2D) honeycomb antiferromagnets driven by pseudogauge fields induced by surface acoustic waves (SAWs) has been investigated. Unlike previous studies where the orbital Hall response of magnons was primarily driven by temperature gradients, we demonstrate that strain-induced pseudoelectric fields generated by Rayleigh-type SAWs can also induce a finite magnon orbital Hall current. In the absence of Dzyaloshinskii-Moriya (DM) interaction, the contribution originates solely from the valley-independent pseudoelectric field ${\mathbf{E}}_1^s$, whereas the valley-contrasting field ${\mathbf{E}}_2^s$ gives no net contribution. When the DM interaction is introduced, the valley degeneracy in the magnon bands is lifted, leading to a population imbalance between the $K$ and $K^{\prime }$ valleys, which activates additional contributions from ${\mathbf{E}}_2^s$, and consequently modifies the anomalous orbital Hall conductivity of magnons. Our results reveal a distinct mechanistic pathway to control magnon orbital transport using SAWs, offering opportunities for valley-orbitronics and magnonic device functionalities in 2D magnetic systems.

The recent surge of interest in magnetism in van der Waals (vdW) crystals has opened opportunities for exploring antiferromagnetic order and spin dynamics in the two-dimensional limit. Here, we present a comprehensive study of the layered antiferromagnetic ${\mathrm{NiCl}}_2$, combining static magnetization, broadband microwave absorption spectroscopy, and tunneling transport measurements. Despite early studies of bulk ${\mathrm{NiCl}}_2$, our systematic approach provides a modern reexamination of its magnetic properties with several new insights. We find nearly identical in-plane and out-of-plane saturation fields once demagnetization corrections are applied, as well as a pronounced spin-flop transition at low fields. The Néel transition temperature ($T_{\mathrm{N}}$) shows minimal anisotropy at low fields but undergoes a distinct crossover between in-plane and out-of-plane field orientations at high fields. Spin resonance experiments reveal strongly anisotropic behavior: robust in-plane antiferromagnetic resonance modes are observed over a broad gigahertz frequency and temperature range, while out-of-plane measurements show suppressed response near $T_{\mathrm{N}}$. This enables the extraction of the effective $g$ factor across a wide temperature window. Furthermore, tunneling magnetoconductance through a thin ${\mathrm{NiCl}}_2$ flake barrier exhibits field-enhanced transmission with clear signatures of the spin-flop and saturation fields. Our findings establish ${\mathrm{NiCl}}_2$ as a model vdW antiferromagnet for studying the interplay of static order, spin dynamics, and tunneling transport, highlighting its potential for future applications in two-dimensional spintronics.

Driving nontopological materials out of equilibrium using time-periodic perturbations, such as circularly polarized laser light, is a compelling way to engineer topological phases. At the same time, topology has traditionally only been considered for crystalline materials. Here we propose an experimentally feasible way of driving monolayer amorphous carbon topological. We show that circularly polarized laser light induces both regular and anomalous edge modes at quasienergies 0 and $\pm \pi$, respectively. We also obtain a complete topological characterization using an energy- and space-resolved topological marker based on the spectral localizer. Additionally, by introducing atomic coordination defects in the amorphous carbon, we establish the importance of the local atomic coordination in topological amorphous materials. Our work establishes amorphous systems, including carbon, as a versatile and abundant playground to engineer topological phases.

Magnetic skyrmioniums, possessing zero net topological charge, are promising candidates for next-generation spintronic devices. Using micromagnetic simulations, we investigate the current-driven dynamics of ferromagnetic (FM) and synthetic antiferromagnetic (SAF) skyrmioniums in granular nanotracks. Local variations in interfacial Dzyaloshinskii–Moriya interaction, anisotropy, and saturation magnetization are found to strongly influence skyrmionium mobility and stability. FM skyrmioniums exhibit pronounced sensitivity to disorder, showing pinning at low current densities and Magnus force induced deformation at high current densities. Their mobility is strongly dependent on grain size: smaller grains promote smoother motion, while larger grains enhance pinning. Moreover, an external magnetic field is found to enhance FM skyrmionium stability by mitigating transverse distortions. In contrast, SAF skyrmioniums display remarkable robustness across a wide range of disorder strengths and current densities due to the cancellation of the Magnus force, maintaining higher longitudinal velocities. Disorder-induced pinning forces hinder the longitudinal motion of both FM and SAF skyrmioniums by introducing energy barriers that suppress their velocity, however, the effect of disorder is weaker for SAF skyrmioniums. These findings establish SAF skyrmioniums as robust, disorder-tolerant candidates for next-generation racetrack memory and spintronic logic devices.

Rare-earth tri-iodides ($R{\mathrm{I}}_3$) are a series of two-dimensional van der Waals (vdW) magnetic materials comprising a layered honeycomb structure. Both the growing interest in vdW magnetic systems and the honeycomb layered structure of $R{\mathrm{I}}_3$ compounds, which is essential for realizing Kitaev physics, motivated us to grow high-quality single crystals of this series of materials and investigate their ground-state magnetic properties. Here, we report the crystal growth, magnetic, and thermodynamic properties of large (centimeter-sized), high-quality crystals of $R{\mathrm{I}}_3$ compounds. The crystal growth uses the physical vapor transport method via self-transport reaction using iodine as a transporting agent. The growth parameters are meticulously reported. The crystallographic parameters are obtained using single-crystal x-ray diffraction. While the $R{\mathrm{I}}_3$ compounds for the lighter rare earths ($R$ = La and Ce) crystallize with an orthorhombic (Cmcm) structure, the structure for the heavier rare earths is trigonal ( $R\overline{3}$ ), analogous to the extensively investigated Kitaev material $\alpha \text{−}{\mathrm{RuCl}}_3$. The density functional theory–based calculations are performed to obtain the eigenfrequencies/eigenvectors of the Raman-active phonon modes for both structure types and compared with the experimental Raman spectra of ${\mathrm{CeI}}_3$ (Cmcm) and ${\mathrm{HoI}}_3$ ( $R\overline{3}$ ). The magnetic behavior examined for the heavier rare-earth-based compounds indicates no signs of long-range magnetic ordering down to 2 K. However, signatures of short-range correlations are seen below 5 K, both in the magnetic susceptibility and specific heat of all the compounds.

We present a systematic investigation of superconductivity in a topological superconductor candidate $T_d{\text{-MoTe}}_2$ in the few-layer limit. By examining multiple mechanically exfoliated samples with different thicknesses, substrates, and crystal qualities, we quantitatively correlate superconducting temperature $\left(T_c\right)$ with disorder, carrier density, carrier type, and mobility. By integrating these experimental findings with first-principles calculations, we reveal the relationship between the band structure and superconductivity in this material. Notably, in two-layer samples we access a highly hole-doped regime that has not been systematically explored in previous experiments, providing a complementary perspective to earlier studies. In this regime, we demonstrate that superconductivity can be realized in a manner consistent with a conventional phonon-mediated $s_{(++)}$-wave pairing.

Topological nodal superconductors (SCs) have attracted considerable interest due to their gapless bulk excitations and exotic surface states. In this paper, by establishing a general framework of the effective theory for multiorbital SCs in the weak-pairing limit, we realize a class of three-dimensional time-reversal ($\mathcal{T}$) invariant Dirac SCs, with their topologically protected gapless Dirac nodes being located at generic momenta. By introducing $\mathcal{T}$-breaking pairing perturbations, we demonstrate the existence of Majorana hinge modes in these Dirac SCs as evidence of their realization of higher-order topology. We also propose a kind of $\mathcal{T}$-breaking Dirac SCs, whose Dirac nodes possess nonzero even chiralities and so are characterized by surface Majorana arcs.

We establish the integrability of a family of Sachdev-Ye-Kitaev (SYK) models with uniform $p$-body interactions. We derive the R-matrix and mutually commuting transfer matrices that generate the Hamiltonians of these models, and obtain their exact eigenspectra and eigenstates. Remarkably, the R-matrix is that of the critical transverse-field Ising chain. This work reveals an unexpected connection between the SYK model, central to many-body quantum chaos, and the critical Ising chain, a cornerstone of statistical mechanics.

We investigate the transport properties of the interface between normal and superconducting Weyl semimetals. We find that the Fermi arcs on the junction interface consist of two types of arc fragments: localized Fermi arcs, composed of states entirely confined to the interface, and resonant Fermi arcs, formed by states partially localized at the interface. The existence of these interface resonant states arises from the interaction between interface Fermi arcs and superconductivity. These resonant states induce an Andreev reflection anomaly, where Andreev reflection is significantly enhanced and its probability reaches unity at a specific momentum space point where the resonant states merge into the bulk continuum. The Andreev reflection anomaly generates an additional supercurrent, which becomes most pronounced when the incident Fermi pocket is tangent to the transmissive one.

We provide insights into the atomistic details of the ultrafast spatially resolved breakdown of the insulating ${\mathrm{M}}_1$ phase in bulk ${\mathrm{VO}}_2$ employing an ab initio technique based on dynamical mean-field theory and time-dependent density-functional theory. We find that the system is initially metallized preferentially along the vanadium-dimer chains, with a subsequent growth of metallic bubbles elongated along the ${\mathrm{C}}_{\mathrm{R}}$ direction. We trace the breakdown of the insulating phase to the two types of oxygen atoms resulting from vanadium dimerization, which produces a nontrivial charge-density modulation in the oxygen-atom chains with significant charge transfer to the interdimer bond. These results, which are in qualitative agreement with experimental data, shed light on the important role of the nonequivalent oxygen atoms in the spatially resolved ultrafast response of this strongly correlated insulator.

When an electron beam is incident from a Weyl semimetal (WSM) onto another material and undergoes reflection, it exhibits a spatial shift. This shift depends on the in-plane wave vectors and displays vortex structures in the incident pocket (the projection of the Fermi surface) or on the pocket edge. According to Yang and He [Phys. Rev. B 110, 195302 (2024)], based on the quantization of Berry flux on the Fermi surface of a type-I WSM, the total vortex number corresponds to the topological charge carried by the Weyl point, while the number of edge vortices equals that of the Fermi arcs connected to the incident pocket. However, when the incident material is a type-II WSM, the Fermi surface of incidence is a hyperboloid (the Fermi pocket is a two-sheeted hyperbola), which is fragmental and nonenclosed. In this case, the quantization condition breaks down and the definition of interface topology requires revision. We introduce a composite loop for the incident sheet comprising two segments: one tracing the sheet edge and the other winding back across the hyperbola in the remote. It is found that the accumulation of reflection shift along the composite loop serves to characterize the interface topology. The edge segment yields both the number of edge vortices and that of Fermi arcs connected to the incident sheet, whereas the crossing segment counts the lost vortices—those absent in the open Fermi surface but expected in a closed one. A vortex loss in one sheet mandates the emergence of an antivortex in the other. Our findings enrich the understanding about topological properties of materials with open Fermi surfaces.

Intermetallic compounds such as ${\mathrm{A}}_2{\mathrm{B}}_7$ alloys are promising candidates for mobile hydrogen storage applications due to their high and reversible hydrogen absorption capacity. We compute the absorption isotherm of ${\mathrm{Nd}}_3{\mathrm{MgNi}}_{14}$ from first principles using a multiscale modeling approach. Absorption sites are identified through a systematic geometrical analysis, and are characterized with density functional theory (DFT) calculations. The absorption site properties are used in room-temperature grand canonical Monte Carlo simulations to predict hydrogen uptake as a function of pressure, leading to a full absorption isotherm in good agreement with experimental data. We show that both hybrid exchange-correlation functionals and zero-point energy corrections are necessary to obtain accurate absorption properties. The analysis of the fully hydrogenated structure with DFT shows considerable volume expansion, which stabilizes the structure at large hydrogen content.

Topological Anderson insulators represent a class of disorder-induced, nontrivial topological states of matter. In this study, we propose a feasible strategy to unveil and design topological Anderson insulators protected by latent symmetries. These are not visible in the original system, but become obvious after performing an isospectral reduction. Using this technique, we design a family of disordered multiatomic chains that exhibit latent chiral symmetry or mirror (inversion) symmetry. Using topological invariants, bulk polarization, and the divergence of localization length of the topological bound edge states in the reduced disordered system, we show how to identify the gapped and ungapped topological Anderson states in the original systems. Our work thus extends the concept of topological Anderson insulating phases protected by geometric symmetries and tenfold-way classification to the various types of latent symmetry cases. Overall, our work paves the way for exploiting topological Anderson insulators in terms of latent symmetries.

While twisted magnonic crystals (MCs) have recently gained attention for their intriguing linear phenomena, such as magnon flat bands, their nonlinear dynamics—particularly the generation of magnonic frequency combs (MFCs)—have remained largely unexplored. In this work, we demonstrate the creation of MFCs in twisted MCs using two-tone microwave excitation. We find that finite twist angles significantly enhance three-magnon interactions, driven by the noncollinear ground-state magnetic configuration induced by interlayer dipole-dipole interactions. The coupling strength of three-magnon interactions exhibits a plateau-like dependence on the twist angle. Moreover, the magnon band structure is modified by twisting, resulting in band gaps diminishing and even vanishing at certain angular ranges. The combination of the two unique roles of twisting reveals an optimal range of twist angles for achieving high-quality MFCs with a large number of comb teeth. Our findings deepen the understanding of nonlinear interactions in twisted MCs and highlight their potential for advancing moiré-based materials in information processing and high-precision metrology.